Apparatus of the type having heating means include, for example, a fixing device for use in an image forming apparatus, such as a copying machine, configured to form an image on a medium to be heated such as a recording sheet. Such a fixing device comprises a heating roller (also referred to as a heating member) having a single or plural heating means therewithin, and a pressurizing roller (also referred to as a pressure member) in contact with the heating roller, wherein: the heating means is caused to generate heat to set the surface temperature of the heating roller to a target temperature (fixing temperature); and a medium to be heated, such as a recording sheet, bearing unfixed toner transferred thereto is passed through the contact region (fixing nip area) defined between the heating roller and the pressurizing roller with its unfixed toner bearing side facing the heating roller, whereby the unfixed toner is fixed under heat and pressure.
A control section, which is configured to control the operation of the image forming apparatus, controls an setting value of electric power to be supplied to cause the heating means to generate heat based on the surface temperature of the heating roller detected by temperature detection means.
Also, components forming the image forming apparatus, including a document reading section and a driver section, need be supplied with power. Since the image forming apparatus is supplied with a constant power from a commercial power source, the power to be supplied to each of the components of the image forming apparatus depending on the status of operation of each component for the image forming apparatus to operate properly is limited to an allowable power value that is lower than a rated power value. For this reason, the aforementioned setting value of electric power to be supplied to the heating means provided inside the heating roller is adjusted within a range not exceeding the allowable power value based on the surface temperature of the heating roller.
Recent image forming apparatus include one which is provided with power control means configured such that when the document reading section provided is in operation, the exposure lamp of the document reading section and the lamp in the heating roller of the fixing device form a series circuit to allow current to pass these lamps, while, when the document reading section is out of operation, the exposure lamp and the lamp in the heating roller form a parallel circuit to allow current to pass through the lamp in the heating roller but cut off passage of current through the exposure lamp (see patent document 1 for example). The art of patent document 1 is also configured such that, when the driving device of the image forming apparatus is out of operation, the series circuit is released to form a parallel circuit and the amounts of powers to be supplied to the exposure lamp and the heating roller lamp are increased.
Patent document 1: Japanese Patent Laid-Open Publication No. HEI 8-286554